Silicone composition and process that is useful for improving the tear strength and the combing strength of an inflatable bag for protecting an occupant of a vehicle

ABSTRACT

The general field of the invention is that of airbags. The invention relates to a process for improving the tear strength and the combing strength of coated fabrics intended for uses in the field of inflatable bags using a silicone composition comprising an additive containing a polyorganosiloxane resin (V) and a calcium carbonate. After coating the composition onto the fabric supports and curing, the coated supports not only have optimum adhesion and crease resistance properties, but also have good properties in terms of combing strength and tear strength.

The general field of the invention is that of silicone coatingcompositions, in particular those of the two-pack or multi-pack type,which cure by polyaddition or hydrosilylation reactions to produce anelastomer as a thin layer. These cured compositions are adapted, interalia, as coatings, for example for the protection or the mechanicalreinforcement of various textile substrates, for instance woven, knittedor nonwoven fibrous supports.

Such silicone coatings are generally obtained by coating the substratefollowed by hardening following from the polyaddition of the unsaturatedgroups (alkenyl groups, e.g. Si-Vi) of a polyorganosiloxane on hydrogensthereof or of another polyorganosiloxane.

These silicone compositions have found a major application in thecoating of flexible—woven, knitted or nonwoven—materials used formanufacturing personal protection bags for the occupants of vehicles,also known as “airbags”.

For further details regarding these personal protection bags or“airbags”, reference may be made especially to French patent FR-A-2 668106.

The present invention also relates to the application of silicones inthe manufacture of such protection bags.

Historically, these bags are formed by a web of synthetic fibre, forexample polyamide (Nylon®), coated on at least one of its faces with alayer of an elastomer such as chloroprene. The presence of such a layeror of such a protective coating is dictated by the fact that the gasesliberated by the gas generator (for example: carbon monoxide, NOx) inthe event of an impact are extremely hot and contain incandescentparticles that are liable to damage the Nylon® bag.

The inner elastomeric protective layer must thus be particularlyresistant to high temperatures and to mechanical stresses. It is alsoimportant for this elastomeric coating to be in the form of a thin,uniform film that adheres fully to the synthetic fabric support, formingthe walls of the airbag.

Silicone compositions have easily supplanted chloroprenes in thisapplication, since it turns out that chloroprenes do not satisfy all theabove-targeted specifications.

However, another constraint has currently emerged and requires newsolutions. The use of gas generators that are more mechanically andthermally aggressive entails additional constraints on the stitching ofthe airbag. These are in addition to the physical constraints associatedwith the deployment of the inflatable bag and may result in ripping ofthe elastomer-coated fabric and opening of these stitches. This resultsin a point of escape of hot gases, arising from the generator, throughthe stitches, giving rise to weak points that are the cause of tearing,combing (fraying) or even bursting of certain airbags. Consequently,airbag manufacturers are in search of silicone elastomeric coatingcompositions for applications that have optimum mechanical properties,especially good tear strength and combing strength (capacity of thecoated fabric to withstand combing of the stitches of the inflatablebag). Specifically, the combing strength is becoming an increasinglyimportant criterion for this industry since the constraints due to thecombing of the stitches of the inflatable bag are comparable to thoseobserved during the deployment of an airbag in service.

One of the major problems currently encountered in the use of fabricscoated with silicone elastomers in airbags lies in the fact that theyhave either good combing strength or good tear strength. Obtaining agood compromise between these two properties, while at the same timemaintaining good properties in terms of adhesion and thinness, isfundamental and is currently the focus of extensive research.Furthermore, airbag manufacturers are also in search of novel solutionsfor reducing their manufacturing costs, especially by usingdecontextured fabrics (reduction of the number of yarns per centimetre),which also requires control of the combing strength and the tearstrength of the fabrics coated with silicone elastomers.

The prior art EP-A-0 533 840 and U.S. Pat. No. 5,296,298 describesilicone compositions for airbag applications.

According to EP-A-0 553 840, these known silicone compositions comprise:

-   -   (A) a polydiorganosiloxane containing at least two alkenyl        groups per molecule,    -   (B) a polyorganohydrogenosiloxane containing at least two        hydrogen atoms linked to silicon in each molecule,    -   (C) a metallic catalyst of the platinum group,    -   (D) an adhesion promoter consisting of an epoxy-functional        organosilicon compound,    -   (E) a mineral filler, the weight amount of which is defined        relative to the amount of the polyorganosiloxane (A),    -   (F) a resin polyorganosiloxane, and optionally    -   (G) a compound that is useful as a curing inhibitor.

However, the said reference only presents solutions for obtaininghomogeneous and adhesive films for airbag coatings and is silent asregards solving the problem mentioned above.

According to U.S. Pat. No. 5,296,298, these silicone compositionscomprise:

-   -   (A) a polydiorganosiloxane containing at least two alkenyl        groups per molecule,    -   (B) a polyorganohydrogenosiloxane containing at least two        hydrogen atoms linked to silicone in each molecule,    -   (C) a silane containing a methacrylic function,    -   (D) an epoxyalkoxysilane,    -   (E) an aluminium chelate, and    -   (F) a metallic catalyst of the platinum group.

In the said reference, the fillers are mentioned only as options, whileproviding solutions only for obtaining silicone films that show goodadhesion to the airbag support. These compositions are not adapted tothe new expectations of airbag manufacturers as regards controlling thecombing strength and tear strength properties.

Document EP-A-0 681 014 describes a silicone composition, which may beapplied especially as an airbag lining and which has for this purposegood properties especially in terms of fire resistance and heatresistance, mechanical properties, ageing behaviour, adhesion andsurface uniformity, the adhesion to textile substrates being moreparticularly desired. The solution proposed by the said inventionconsists in using:

-   -   a silicone coating composition consisting of a mixture formed        from:    -   (1) at least one polyorganosiloxane containing, per molecule, at        least two C2-C6 alkenyl groups linked to silicon,    -   (2) at least one polyorganosiloxane containing, per molecule, at        least two hydrogen atoms linked to silicon,    -   (3) a catalytically effective amount of at least one catalyst,        composed of at least one metal belonging to the platinum group,    -   (4) an adhesion promoter,    -   (5) optionally, a mineral filler,    -   (6) optionally, at least one curing inhibitor, and    -   (7) optionally, at least one polyorganosiloxane resin,    -   in which composition the adhesion promoter consists exclusively        of an at least ternary combination of the following ingredients:    -   (4-1) at least one alkoxylated organosiloxane containing, per        molecule, at least one C2-C6 alkenyl group,    -   (4-2) at least one organosilicon compound comprising at least        one epoxy radical, and    -   (4-3) at least one metal chelate M and/or a metal alkoxide of        general formula: M(OJ)n, with n=valency of M and J=linear or        branched C1-C8 alkyl, M being chosen from the group formed by:        Ti, Zr, Ge, Li, Mn, Fe, Al and Mg.

It should be noted that a reinforcing filler such as a pyrogenic silicais always present in the experimental section of document EP-A-0 681014. These compositions are not adapted to the new expectations ofairbag manufacturers as regards controlling the combing strength andtear strength properties.

The present invention is directed towards overcoming the drawbacks ofthe prior art. In this perspective, one of the essential objectives ofthe invention is to provide a process for improving the combing strengthand the tear strength of a woven, knitted or nonwoven fibrous support.These supports treated by means of the process according to theinvention are useful especially for applications in the field ofinflatable safety bags for vehicles, or airbags, which have not onlyoptimum properties in terms of adhesion, thinness, lightness andresistance to creasing and to abrasion (“scrub” test), but also goodcombing strength and tear strength properties.

A second objective of the invention is to provide a silicone coatingcomposition that may be cured by polyaddition reactions, which is usefulespecially for applications in the field of inflatable safety bags forvehicles, or airbags, which has after curing optimum properties in termsof adhesion, thinness, lightness and resistance to creasing and toabrasion (“scrub” test), but also good combing strength and tearstrength properties.

A third objective of the invention is to provide a silicone coatingcomposition that may be cured by polyaddition reactions, for airbags,which is easy to use and to apply, and which is also economical.

Finally, another objective of the invention is to allow a reduction inthe cost of the coating so as to broaden the field of use of thesilicone coating and thus to exploit the advantageous properties of thistype of coating in applications that are at the present time excludedfrom the field of application for reasons of cost.

These objectives, among others, are achieved by the invention, whichcomprises a process for improving the combing strength and the tearstrength of a woven, knitted or nonwoven fibrous support, comprising thefollowing steps:

-   -   a) the preparation of a curable silicone coating composition (A)        comprising:    -   components (a-1) or (a-2):    -   (a-1) corresponding to at least one polyorganosiloxane that may        be cured by the action of a catalyst based on at least one        organic peroxide, and    -   (a-2) corresponding to a polyorganosiloxane blend that may be        cured by polyaddition reactions, comprising:        -   at least one polyorganosiloxane (I) containing, per            molecule, at least two C2-C6 alkenyl groups linked to            silicon, and        -   at least one polyorganosiloxane (II) containing, per            molecule, at least two hydrogen atoms linked to silicon,    -   an effective amount of curing catalyst consisting: when (a-1) is        used, of at least one organic peroxide, and when (a-2) is used,        of at least one metal (or compound) of the platinum group,    -   optionally, at least one adhesion promoter (IV), and    -   an additive system (B) for improving the combing strength and        the tear strength, the constituents of which are added        sequentially or simultaneously, comprising a mixture of:        -   at least one polyorganosiloxane resin (V) present at up to            60% by weight relative to the total weight of the mixture            and optionally mixed with at least one polyorganosiloxane            serving as diluent, and        -   calcium carbonate (CaCO₃) present at up to 30% by weight            relative to the total weight of the mixture;    -   b) the application of at least 10 g/m², preferably at least 20        g/m² and more preferably at least 30 g/m², to one or two faces        of a woven, knitted or nonwoven fibrous support of the silicone        coating composition (A) prepared in step a), and    -   c) the curing of the deposit formed in step b) to form an        elastomer by heating to a temperature that may be up to 210° C.,        by electromagnetic radiation, in particular by infrared        radiation.

It is to the Applicant's credit to have demonstrated the importance ofthe additive system (B) for the purpose of controlling the combingstrength and the tear strength of a woven, knitted or nonwoven fibroussupport. The calcium carbonate does not need to undergo acompatibilization treatment (by heating or surface treatment) in orderto be used in the system (B) and therefore cannot be likened to a simplesemi-reinforcing filler. It was not at all foreseeable that thecombination of the resin (V) and of calcium carbonate, in animplementation not requiring a compatibilization treatment, wouldultimately lead to such a marked improvement in the combing strength andtear strength properties of a woven, knitted or nonwoven fibrous supportespecially for applications in airbags.

This is all the more surprising since this gain does not become lost atthe expense of the other hardness, mechanical strength, surfaceuniformity and heat resistance properties of the silicone coating.

The polyorganosiloxane (a1) that is curable by the action of a catalystbased on at least one organic peroxide is advantageously a productcontaining siloxyl units of formula: $\begin{matrix}{R_{a}^{1}{SiO}\frac{\left( {4 - a} \right)}{2}} & \left( {I\text{-}1} \right)\end{matrix}$in which:

-   -   the symbols R¹, which may be identical or different, represent a        hydrocarbon-based group containing from 1 to 12 carbon atoms and        preferably from 1 to 8 carbon atoms, which is optionally        substituted, and    -   a is 1, 2or3.

Preferably, the symbols R¹ are chosen from:

-   -   methyl, ethyl, propyl, butyl, hexyl and dodecyl groups,    -   cycloalkyl groups, for instance cyclohexyl,    -   alkenyl groups, for instance vinyl, allyl, butenyl and hexenyl        groups,    -   aryl groups, for instance phenyl, tolyl and aralkyl groups such        as β-phenylpropyl, and    -   the groups mentioned above in which one or more hydrogen atoms        are replaced with one or more halogen atom, a cyano group or a        cyano group equivalent, for instance a chloromethyl,        trifluoropropyl or cyanoethyl.

Even more preferentially, the polyorganosiloxanes (a-1) are terminatedat the chain ends with trimethylsilyl, dimethylvinyl,dimethylhydroxysilyl or trivinylsilyl units.

In one particularly advantageous embodiment, the polyorganosiloxanes(a-1) contain at least two alkenyl groups per molecule.

Among the organic peroxides that may be used according to the invention,mention may be made of benzoyl peroxide, bis(p-chlorobenzoyl) peroxide,bis(2,4-dichlorobenzoyl)peroxide, dicumyl peroxide, di-t-butyl peroxide,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, t-butyl perbenzoate,t-butylcumyl peroxide, halogenated derivatives of the peroxidesmentioned above, for instance bis(2,4-dichlorobenzoyl) peroxide,1,6-bis(p-toluoylperoxycarbonyloxy)hexane,1,6-bis(benzoylperoxycarbonyloxy)hexane,1,6-bis(p-toluoylperoxycarbonyloxy)butane and1,6-bis(2,4-dimethylbenzoylperoxycarbonyloxy)hexane.

According to one preferred embodiment of the process according to theinvention, the curable silicone coating composition (A) used comprisespolyorganosiloxanes that may be cured by polyaddition reactions. Thiscomposition (A) comprises a mixture formed from:

-   -   (a) at least one polyorganosiloxane (I) containing, per        molecule, at least two C2-C6 alkenyl groups linked to silicon,    -   (b) at least one polyorganosiloxane (II) containing, per        molecule, at least two hydrogen atoms linked to silicon,    -   (c) a catalytically effective amount of at least one catalyst        (III), composed of at least one metal belonging to the platinum        group,    -   (d) at least one adhesion promoter (IV),    -   (e) an additive system (B) for improving the combing strength        and the tear strength, the constituents of which are added        sequentially or simultaneously, comprising a mixture formed        from:        -   at least one polyorganosiloxane resin (V) present at up to            60% by weight relative to the total weight of the mixture            and optionally mixed with at least one polyorganosiloxane            serving as diluent, and        -   calcium carbonate (CaCO₃) present at up to 30% by weight            relative to the total weight of the mixture;    -   (f) optionally, at least one curing inhibitor (VI),    -   (h) optionally, at least one coloration additive (VII), and    -   (i) optionally, at least one additive (VIII) for improving the        fire resistance.

In accordance with one preferred arrangement of the process according tothe invention, the amount of calcium carbonate in the additive system(B) is between 4% and 26% by weight and even more preferably between 10%and 24% by weight relative to the total weight of the mixture.

The choice of these specific intervals is one of the determiningcriteria as regards resolving the problem of improving the combingstrength and tear strength properties.

Another important criterion is the presence of the polyorganosiloxaneresin (V) in the additive system (B) present at up to 60% by weight,preferably up to 40% by weight and even more preferably in a proportionof from 11% to 30% by weight or from 15% to 25% by weight, relative tothe total weight of the mixture.

We have also discovered that, in order to obtain an optimum effect, itsuffices to perform the process according to the invention with anadditive system (B) comprising 5% to 30% by weight of polyorganosiloxaneresin (V) and 5% to 25% by weight of calcium carbonate relative to thetotal weight of the mixture.

The resin (V) preferably comprises at least one alkenyl residue in itsstructure. According to one preferred mode, the polyorganosiloxane resin(V) comprises siloxyl units Q of formula SiO_(4/2).

According to another particular mode, the polyorganosiloxane resin (V)comprises in its structure from 0.1% to 20% by weight preferably greaterthan 4% by weight and of alkenyl group(s), the said structure containingidentical or different siloxyl units of type M, identical or differentsiloxyl units of type(s) T and/or Q, and optionally siloxyl units oftype D.

In a particularly preferred manner, the polyorganosiloxane resin (V)comprises at least 2% by weight and preferably at least 5% by weight ofsiloxyl units of type Q.

These resins (V) are well-known and commercially available branchedorganopolysiloxane oligomers or polymers. They are in the form ofsolutions, preferably siloxane solutions. They have in their structureat least two different units chosen from those of formulae R₃SiO_(0.5)(unit M), R₂SiO (unit D), RSiO_(1.5) (unit T) and SiO₂ (unit Q), atleast one of these units being a unit T or Q.

The radicals R are identical or different and are chosen from linear orbranched C1-C6 alkyl radicals, C2-C4 alkenyl radicals, phenyl and3,3,3-trifluoropropyl. Mention may be made, for example, of: as alkylradicals R, methyl, ethyl, isopropyl, tert-butyl and h-hexyl radicals,and as alkenyl radicals R, vinyl radicals.

It should be understood that in the resins (V) of the abovementionedtype, some of the radicals R are alkenyl radicals.

As examples of branched organopolysiloxane oligomers or polymers,mention may be made of resins MQ, resins MDQ, resins TD and resins MDT,the alkenyl functions possibly being borne by the units M, D and/or T.As examples of resins that are particularly suitable, mention may bemade of vinyl MDQ resins with a weight content of vinyl group of between0.2% and 10% by weight.

Without this being limiting, it may be considered that the adhesionpromoter (IV) exclusively comprises:

-   -   (IV.1) at least one alkoxylated organosilane containing, per        molecule, at least one C2-C6 alkenyl group,    -   (IV.2) at last one organosilicon compound comprising at least        one epoxy radical, and    -   (IV.3) at least one metal chelate M and/or a metal alkoxide of        general formula:    -   M(OJ)n, with n=valency of M and J=linear or branched C1-C8        alkyl,    -   M being chosen from the group formed by: Ti, Zr, Ge, Li, Mn, Fe,        Al and Mg.

In accordance with one preferred arrangement of the invention, thealkoxylated organosilane (IV.1) of the promoter (IV) is selected fromthe products having the following general formula:

in which formula:

-   -   R1, R2 and R3 are identical or different hydrogenated or        hydrocarbon-based radicals and represent hydrogen, a linear or        branched C1-C4 alkyl or a phenyl optionally substituted with at        least one C1-C3 alkyl,    -   U is a linear or branched C1-C4 alkylene,    -   W is a valency bond,    -   R4 and R5 are identical or different radicals and represent a        linear or branched C1-C4 alkyl radical,    -   x′=0 or 1, and    -   x=0 to 2.

Without this being limiting, it may be considered that thevinyltrimethoxysilane is a particularly suitable compound (IV.1).

As regards the organosilicon compound (IV.2), it is envisaged inaccordance with the invention to choose it from:

-   -   a) either the products (IV.2a) corresponding to the following        general formula:        in which formula:    -   R6 is a linear or branched C1-C4 alkyl radical,    -   R7 is a linear or branched alkyl radical,    -   y is equal to 0, 1, 2 or 3, and    -   X being defined by the following formula:        with:    -   E and D, which are identical or different radicals chosen from        linear or branched C1-C4 alkyls,    -   z, which is equal to 0 or 1,    -   R8, R9 and R10, which are identical or different radicals        representing hydrogen or a linear or branched C1-C4 alkyl, and    -   R8 and R9 or R10 alternatively possibly constituting, together        and with the two carbons bearing the epoxy, a 5- to 7-membered        alkyl ring,    -   b) or from the products (IV.2b) consisting of epoxy-functional        polydiorganosiloxanes comprising:    -   (i) at least one siloxyl unit of formula: $\begin{matrix}        {X_{p}G_{q}{SiO}\frac{4 - \left( {p + q} \right)}{2}} & \left( {{IV}{.2}\quad{b1}} \right)        \end{matrix}$        in which formula:    -   X is the radical as defined above for formula (IV.2a)    -   G is a monovalent hydrocarbon-based group, free of unfavourable        action on the activity of the catalyst and chosen from alkyl        groups containing from 1 to 8 carbon atoms inclusive, optionally        substituted with at least one halogen atom, and also from aryl        groups,    -   p=1 or2,    -   q=0, 1 or2,    -   p+q =1, 2 or 3, and    -   (2i) optionally at least one siloxyl unit of formula:        $\begin{matrix}        {G_{r}{SiO}\frac{4 - r}{2}} & \left( {{IV}{.2}\quad{b2}} \right)        \end{matrix}$        in which formula G has the same meaning as above and r is equal        to 0, 1, 2 or 3.

As regards the last compound (IV.3) of the adhesion promoter (IV) of thesilicone composition according to the invention, the preferred productsare those for which the metal M of the chelate and/or of the alkoxide(IV.3) is chosen from the following list: Ti, Zr, Ge, Li or Mn. Itshould be pointed out that titanium is more particularly preferred. Itmay be combined, for example, with an alkoxy radical such as butoxy.

The adhesion promoter (IV) may be formed from:

-   -   (IV.1) alone    -   (IV.2) alone    -   (IV.1)+(IV.2)        according to two preferred embodiments:    -   (IV.1)+(IV.3)    -   (IV.2)+(IV.3)        and finally, according to the most preferred embodiment:        (IV.1)+(IV.2)+(IV.3).

According to the invention, an advantageous combination for forming theadhesion promoter is as follows:

-   -   vinyltrimethoxysilane (VTMO), 3-glycidoxypropyltrimethoxysilane        (GLYMO) and butyl titanate.

In quantitative terms, it may be pointed out that the weight proportionsbetween (IV.1), (IV.2) and (IV.3), expressed as weight percentagesrelative to the total of the three, are as follows:

-   -   (IV.1)≧10%, preferably between 15 and 70% and even more        preferably between 25 and 65%,    -   (IV.2)≦90%, preferably between 70 and 15% and even more        preferably between 65 and 25%, and    -   (IV.3)≧1%, preferably between 5 and 25% and even more preferably        between 8 and 18%,    -   it being understood that the sum of these proportions of (IV.1),        (IV.2) and (IV.3) is equal to 100%.

For better adhesion properties, the weight ratio (IV.2):(IV.1) ispreferably between 2:1 and 0.5:1, the ratio 1:1 being more particularlypreferred.

Advantageously, the adhesion promoter (IV) is present in a proportion offrom 0.1% to 10%, preferably 0.5% to 5% and even more preferably 1% to3% by weight relative to all of the constituents of composition (A).

The polyorganosiloxane (I) is one of the essential constituents ofcomposition (A) for the mode of curing by polyaddition reactions.Advantageously, it is a product comprising:

-   -   (i) siloxyl units of formula: $\begin{matrix}        {R_{a}^{1}Z_{b}{SiO}\frac{4 - \left( {a + b} \right)}{2}} & \left( {I\text{-}1} \right)        \end{matrix}$        in which:    -   the symbols R¹ represent an alkenyl group, preferably vinyl or        allyl,    -   the symbols Z, which may be identical or different, each        represent a monovalent hydrocarbon-based group, free of        unfavourable action on the activity of the catalyst and chosen        from alkyl groups containing from 1 to 8 carbon atoms inclusive,        optionally substituted with at least one halogen atom, and also        from aryl groups,    -   a is 1 or 2, b is 0, 1 or 2 and the sum a+b is equal to 1, 2 or        3, and optionally    -   (ii) other siloxyl units of formula: $\begin{matrix}        {{Zc}\quad{SiO}\frac{4 - c}{2}} & \left( {I\text{-}2} \right)        \end{matrix}$        in which:    -   Z has the same meaning as above and c is 0, 1, 2 or 3.

This polydiorganosiloxane (I) may have a viscosity at least equal to 200mPa.s and preferably less than 200,000 mPa.s.

All the viscosities concerned in the present specification correspond toa dynamic viscosity magnitude that is measured, in a manner that isknown per se, at 25° C.

The polyorganosiloxane (I) may be formed solely from units of formula(I-1) or may contain, in addition, units of formula (I-2). Similarly, itmay have a linear, branched, cyclic or network structure. Z is generallychosen from methyl, ethyl and phenyl radicals, 60 mol % (or in numericalterms) at least of the radicals Z being methyl radicals. Examples ofsiloxyl units of formula (I-1) are vinyldimethylsiloxyl,vinylphenylmethylsiloxyl, vinylmethylsiloxyl and vinylsiloxyl units.

Examples of siloxyl units of formula (1-2) are the units SiO_(4/2),dimethylsiloxyl, methylphenylsiloxyl, diphenylsiloxyl, methylsiloxyl andphenylsiloxyl. Examples of polyorganosiloxanes (I) are linear and cycliccompounds, for instance: dimethyl-polysiloxanes containingdimethylvinylsilyl end groups, (methylvinyl)(dimethyl)-polysiloxanecopolymers containing trimethylsilyl end groups,(methylvinyl)(dimethyl)-polysiloxane copolymers containingdimethylvinylsilyl end groups and cyclic methylvinylpolysiloxanes.

Advantageously, the polyorganosiloxane (II) comprises siloxyl units offormula: $\begin{matrix}{H_{d}L_{e}{SiO}\frac{4 - \left( {d + e} \right)}{2}} & \left( {{II}\text{-}1} \right)\end{matrix}$in which:

-   -   the groups L, which may be identical or different, each        represent a monovalent hydrocarbon-based group, free of        unfavourable action on the activity of the catalyst and chosen,        preferably, from an alkyl group containing from 1 to 8 carbon        atoms inclusive, optionally substituted with at least one        halogen atom, advantageously from methyl, ethyl, propyl and        3,3,3-trifluoropropyl groups, an aryl group, and advantageously        a xylyl, tolyl or phenyl radical,    -   d is 1 or2, e is 0, 1 or2, the sum d+e is equal to 1,2 or 3, and    -   optionally, at least some of the other units being units of mean        formula: $\begin{matrix}        {L_{g}{SiO}\frac{4 - g}{2}} & \left( {{II}\text{-}2} \right)        \end{matrix}$        in which the groups L have the same meaning as above and g is        equal to 0, 1, 2 or 3.

The dynamic viscosity of this polyorganosiloxane (II) is at least equalto 10 mPa.s and preferably between 20 and 1000 mPa.s. Thepolyorganosiloxane (II) may be formed solely from units of formula(II-1) or may also comprise units of formula (II-2). Thepolyorganosiloxane (II) may have a linear, branched, cyclic or networkstructure. The group L has the same meaning as the group Z above.Examples of units of formula (II-1) are H(CH₃)₂SiO_(1/2), HCH₃SiO_(2/2)and H(C₆H₅)SiO_(2/2).

The examples of units of formula (II-2) are the same as those givenabove for the units of formula (I-2).

Examples of polyorganosiloxanes (II) are linear and cyclic compounds,for instance:

-   -   dimethylpolysiloxanes containing hydrogenodimethylsilyl end        groups,    -   copolymers containing (dimethyl)(hydrogenomethyl)polysiloxane        units containing trimethylsilyl end groups,    -   copolymers containing (dimethyl)(hydrogenomethyl)polysiloxane        units containing hydrogenodimethylsilyl end groups,    -   hydrogenomethylpolysiloxanes containing trimethylsilyl end        groups,    -   cyclic hydrogenomethylpolysiloxanes.

The compound (II) may optionally be a mixture of a dimethylpolysiloxanecontaining hydrogenodimethylsilyl end groups and of a polyorganosiloxanebearing at least three functions SiH (hydrogenosiloxyle).

The ratio of the number of hydrogen atoms linked to silicon in thepolyorgano-siloxane (II) to the total number of groups containingalkenyl unsaturation of the polyorganosiloxane (I) and of the resin (V)is between 0.4 and 10 and preferably between 0.6 and 5.

The bases of silicone polyaddition compositions may comprise only linearpolyorganosiloxanes (I) and (II), for instance those described inpatents: U.S. Pat. No. 3,220,972, U.S. Pat. No. 3,697,473 and U.S. Pat.No. 4,340,709 or may comprise both branched or networkpolyorganosiloxanes (I) and (II), for instance those described inpatents: U.S. Pat. No. 3,284,406 and U.S. Pat. No. 3 434 366.

According to one particular embodiment, the following are used:

-   -   at least one linear polyorganosiloxane (I) comprising chains        formed from units of formula (I-2) in which c=2, blocked at each        of their ends with units of formula (I-1) in which a=1 and b=2,        and    -   at least one linear polyorganosiloxane (II) comprising in its        structure at least three hydrogen atoms linked to silicon,        located in the chains and/or at chain ends;        -   and even more particularly:    -   at least one linear polyorganosiloxane (I) comprising chains        formed from units of formula (I-2) in which c=2, blocked at each        of their ends with units of formula (I-1) in which a=1 and b=2,        and    -   at least one linear polyorganosiloxane (I) comprising chains        formed from units of formula (II-1) in which d=1 and e=1 and        optionally units of formula (II-2) in which g=2, blocked at each        of their ends with units of formula (II-1) in which d=1 and e=2.

The catalysts (III) are also well known. The metals of the platinumgroup are those known under the name platinoids, this term combining,besides platinum, ruthenium, rhodium, palladium, osmium and iridium.Platinum and rhodium compounds are preferably used. Complexes ofplatinum and of an organic product described in patents U.S. Pat. No.3,159,601, U.S. Pat. No. 3,159,602, U.S. Pat. No. 3,220,972 and Europeanpatents EP-A-0 057 459, EP-A-0 188 978 and EP-A-0 190 530, and complexesof platinum and of vinylorganosiloxanes described in patents U.S. Pat.No. 3,419,593, U.S. Pat. No. 3,715,334, U.S. Pat. No. 3,377,432 and U.S.Pat. No. 3,814,730 may be used in particular. The catalyst that isgenerally preferred is platinum. In this case, the weight amount ofcatalyst (III), calculated by weight of platinum metal, is generallybetween 2 and 400 ppm, preferably between 5 and 200 ppm on the basis ofthe total weight of the polyorganosiloxanes (I) and (II).

Advantageously, the process according to the invention uses a siliconecomposition (A) comprising at least one addition reaction retardant (VI)(curing inhibitor) and is chosen from the following compounds:

-   -   polyorganosiloxanes substituted with at least one alkenyl that        may optionally be in cyclic form, tetramethylvinyltetrasiloxane        being particularly preferred,    -   pyridine,    -   organic phosphines and phosphites,    -   unsaturated amides,    -   alkyl maleates, and    -   acetylenic alcohols.

These acetylenic alcohols (Cf. FR-B-1 528 464 and FR-A-2 372 874), whichform part of the preferred hydrosilylation-reaction thermal blockers,have the formula:

in which formula:

-   -   R′ is a linear or branched alkyl radical or a phenyl radical;    -   R″ is H or a linear or branched alkyl radical or a phenyl        radical; the radicals R′, R″ and the carbon atom α to the triple        bond possibly forming a ring;    -   the total number of carbon atoms contained in R′ and R″ being at        least 5 and preferably from 9 to 20.

The said alcohols are preferably chosen from those with a boiling pointof greater than 250° C. Examples that may be mentioned include:

-   -   1-ethynyl-1-cyclohexanol;    -   3-methyl-1-dodecyn-3-ol;    -   3,7,11-trimethyl-1-dodecyn-3-ol;    -   1,1-diphenyl-2-propyn-1-ol;    -   3-ethyl-6-ethyl-1-nonyn-3-ol;    -   2-methyl-3-butyn-2-ol;    -   3-methyl-1-pentadecyn-3-ol.

These α-acetylenic alcohols are commercial products.

Such a retardant (VI) is present in a proportion of up to 3000 ppm andpreferably in a proportion of from 100 to 1000 ppm relative to the totalweight of the organopolysiloxanes (I) and (II).

The present invention also relates to the silicone coating composition(A) that is curable by polyaddition reactions to improve the combingstrength and the tear strength of a woven, knitted or nonwoven fibroussupport, comprising a mixture formed from:

-   -   (a) at least one polyorganosiloxane (I) containing, per        molecule, at least two C2-C6 alkenyl groups linked to silicon,    -   (b) at least one polyorganosiloxane (II) containing, per        molecule, at least two hydrogen atoms linked to silicon,    -   (c) a catalytically effective amount of at least one catalyst        (III), composed of at least one metal belonging to the platinum        group,    -   (d) at least one adhesion promoter (IV),    -   (e) an additive system (B) for improving the combing strength        and the tear strength, the constituents of which are added        sequentially or simultaneously to the mixture, comprising a        mixture of:    -   at least one polyorganosiloxane resin (V) present at up to 60%        by weight relative to the total weight of the mixture and        optionally mixed with at least one polyorganosiloxane serving as        diluent, and    -   calcium carbonate (CaCO₃) present at up to 19% by weight        relative to the total weight of the mixture;    -   (f) optionally, at least one curing inhibitor (VI),    -   (h) optionally, at least one coloration additive (VII), and    -   (i) optionally, at least one additive (VIII) for improving the        fire resistance.

As additive (VIII) for improving the fire resistance, examples that maybe mentioned include compounds containing a phenyl group substitutedwith an amino (secondary or tertiary) group. Examples of such additivesare found in the reference U.S. Pat. No. 5,516,938. The useful amountsof such additives are generally between 0.01 and 1 part by weightrelative to the total amount of the composition.

The other constituents of this composition (A) are as defined in theprocess according to the invention.

According to another of its aspects, the present invention relates to aprecursor system {two-pack (C)} for the silicone composition describedabove. Such a precursor system is in two separate parts A and B, whichare intended to be mixed together to form the composition, one of theseparts A or B comprising the catalyst (III) and only onepolyorganosiloxane species (I) or (II).

Yet another characteristic of this precursor system (C) is that theresin (V) may be used in part A or part B or in both parts A and B, thecatalyst (III) not needing to be present in part A or part B containingthe polyorganosiloxane (II) and the resin (V).

In the case of the promoter system (IV-1) (IV-2) (IV-3), anothercharacteristic of this precursor system is that its part A or Bcontaining the polyorganosiloxane is free of compounds (IV-3) of thepromoter (IV) and that its part A or B including the compound (IV-1) ofthe promoter (IV) does not comprise the catalyst (III).

The viscosity of the parts A and B and of their mutual mixture may beadjusted by varying the amounts of the constituents and by selectingpolyorganosiloxanes of different viscosities.

Once mixed together, the parts A and B form a ready-to-use siliconecomposition, which may be applied to the support by any suitable coatingmeans (for example by doctor blade or roll). A final deposited thicknessafter curing of between 25 and 300 μm and especially between 50 and 200μm will generally be targeted. It is not necessary to have a uniformthickness, since, if the surface of the support is not regular, this mayresult in an irregular deposition. The compounds according to theinvention are heat-cured and/or cured by electromagnetic radiation(radiation of accelerated electrons or “electron beam”).

The compositions according to the invention may be used for covering orcoating flexible supports, especially woven, knitted or nonwoven fibroustextiles, and preferably woven, knitted or nonwoven supports made ofsynthetic fibres, advantageously of polyester or polyamide.

The invention is also directed towards a woven, knitted or nonwovenfibrous support coated on one or two faces with an elastomer that may beobtained:

a) by applying at least 10 g/m² onto one or two faces of a woven,knitted or nonwoven fibrous support of the silicone coating composition(A) described above or of the composition resulting from mixing theparts A and B of the two-pack system (B) described above, and

-   -   curing the deposit formed in the preceding step to form an        elastomer by heating to a temperature that may be up to 210° C.        or by electromagnetic radiation, in particular by infrared        radiation, or    -   b) by the process according to the invention described above.

According to one preferred mode of the invention, the fibrous support isa fabric with an open contexture having a porosity >10 l/dm²/minaccording to ISO standard 9237.

Another aspect of the invention concerns an inflatable bag forprotecting an occupant of a vehicle, formed from a support coatedaccording to the procedure of the invention described above.

The invention also relates to the use of the two-pack system (B)according to the invention, of a curable silicone coating composition(A) according to the invention for coating the woven, knitted ornonwoven fibrous support. Preferably, these supports are intended toform inflatable bags for protecting the occupants of vehicles. In onepreferred embodiment, the support is a fabric with an open contexturehaving a porosity >10 l/dm²/min according to ISO standard 9237.

The covering or coating of at least one of the faces of the flexiblesupport material, especially textile (for example polyamide fabric) isuseful for manufacturing technical fabrics such as, especially,inflatable bags for the personal protection of the occupants ofvehicles, in the event of an impact, tent webs, parachute webs and thelike.

In this context, the compositions or the process according to theinvention are found to be noteworthy not only for coating supportsconventionally used especially in the manufacture of inflatable bags,but also for coating supports with an open contexture. The term “supportwith an open contexture” means supports with a porosity >10 I/dm²/minaccording to ISO standard 9237. In the case of a fabric, the opencontexture may especially be defined as corresponding to a number ofwarp and weft yarns per centimetre, the sum of which is less than orequal to 36.

As fabrics that are particularly recommended in the context of thepresent invention, mention will generally be made of fabrics whoseuncoated weight is less than 200 g/m² and especially less than or equalto 160 g/m². Such fabrics, especially polyamide fabrics, having from16×16 to 18×18 yarns/cm may thus be mentioned, for example fabrics of470 dtex (decitex) having these characteristics.

It will be noted that substrates, especially fabrics, formed fromtechnical textile fibres, i.e. textile fibres whose properties areimproved compared with standard fibres, for example increased fastness,in order to impart particular properties or properties that arereinforced as a function of the applications of the coated support orfabric, may also be used.

For the coating of supports with an open contexture, it will bepreferred to use compositions comprising oil (I) with a viscosity ofbetween 10 000 and 200 000 mPa.s, especially between 30 000 and 170 000mPa.s and in particular between 40 000 and 120 000 mpa.s, and resin (V)comprising units Q, especially at least 2% by weight of such units,preferably at least 5% and in particular from 5% to 12%.

A subject of the invention is thus also such a flexible support,especially a textile support, coated in accordance with the inventionand thus possibly having the characteristics and properties indicatedabove.

By virtue of the properties and characteristics indicated above,inflatable bags for personal protection of the occupants of a vehiclemay be made from fabrics of open contexture as described above, inparticular polyamide or polyester fabrics, which, once coated, have goodcombing strength and tear strength, a weight of less than or equal to200 g/m², and moreover having optimum properties especially in terms ofimpermeability, heat protection, porosity and pliability. This makes itpossible to produce lighter inflatable bags for an equivalent thicknessof coating, which have better performance qualities and are lessexpensive than bags made from the coated fabrics of the prior art. It isthus possible, for an equivalent weight, to increase the thickness ofcoating and improve the impermeability and heat protection.

In general, the coating that is concerned herein may correspond to thedeposition of a single layer onto at least one of the faces of theflexible support material (primary coating). However, it may alsoconcern the deposition of a second layer or optionally a third layeronto at least one of the faces of the already-coated support material(secondary coating) to have in total the desired thickness that ensuresthe best possible performance qualities in terms of impermeability andfavourable feel characteristics.

The examples that follow, of the preparation of compositions and oftheir application as coating for polyamide fabric according to theprocess of the invention, will allow the invention to be understood moreclearly and will allow its advantages and implementation variants to behighlighted. The performance qualities of the products resulting fromthe process according to the invention will be illustrated by means ofcomparative tests.

EXAMPLES

In these examples, the viscosity is measured using a Brookfieldviscometer according to the indications of AFNOR standard NFT-76-106 ofMay 1982.

Example 1

1) Definition of the Constituents:

-   -   polyorganosiloxane (I): polydimethylsiloxane oil blocked at each        of the ends of the chains with a (CH₃)₂ViSiO_(0.5) unit, having        a viscosity of 100 000 mPa.s and containing 0.003 Si-Vi function        per 100 g of oil [constituent referred to hereinbelow as        high-viscosity oil (I)];    -   polyorganosiloxane (I-a): a polydimethylsiloxane oil blocked at        each of the ends of the chains with a (CH₃)₂ViSiO_(0.5) unit,        having a viscosity of 10 000 mPa.s and containing 0.005 Si-Vi        residue per 100 g of oil [constituent referred to hereinbelow as        low-viscosity oil (I)];    -   polyorganosiloxane referred to hereinbelow as diluent (A): a        polydimethylsiloxane oil blocked at each of the ends of the        chains with a (CH₃)₂ViSiO_(0.5) unit, having a viscosity of 60        000 mPa.s;    -   polyorganosiloxane referred to hereinbelow as diluent (B): a        polydimethylsiloxane oil blocked at each of the ends of the        chains with a (CH₃)₂ViSiO_(0.5) unit, having a viscosity of 3500        mPa.s;    -   polyorganosiloxane (II): poly(dimethyl)(hydrogenomethyl)siloxane        oil blocked at each of the ends of the chains with a        (CH₃)₂HSiO_(0.5) unit, having a viscosity of 25 mPa.s and        containing in total 0.7 Si—H function per 100 g of oil        (including 0.6 Si—H function located in the chain) [constituent        referred to hereinbelow as oil (II)];    -   catalyst (III): platinum metal, introduced in the form of an        organometallic complex containing 10% by weight of platinum        metal, known under the name Karstedt catalyst [constituent        referred to hereinbelow as platinum of the catalyst (III)];    -   adhesion promoters (IV): mixture composed of:        -   (IV-1) vinyltrimethoxysilane (VTMO),        -   (IV-2) glycidoxypropyltrimethoxysilane (GLYMO), and        -   (IV-3) butyl titanate Ti(OBu)4 (TBT);    -   resin (V): polyorganosiloxane of formula MM^(Vi)DD^(Vi)Q        containing 0.8% by weight of vinyl groups (Vi) and consisting of        27% by weight of (CH₃)₃SiO_(0.5) units, 0.15% by weight of        (CH₃)₂ViSiO_(0.5) units, 60% by weight of (CH₃)₂SiO units, 2.4%        by weight of (CH3)ViSiO units and 9.6% by weight of SiO₂ units;    -   calcium carbonate (1), CaCO₃ (Albacar® 5970), precipitated        calcium carbonate, equivalent mean diameter: 2 μm and acicular        shape which has not undergone a compatibilization treatment        (heating or surface functionalization).    -   calcium carbonate (2), CaCO₃ (Socal® 31 sold by the company        Solvay), equivalent mean diameter: 0.07 μm;    -   calcium carbonate (3), CaCO₃ (BLR3® 31 sold by the company        Omya), equivalent mean diameter: 0.07 μm    -   filler (VII-C): ground quartz with a mean particle size of about        2.5 μm and a BET surface area of about 3 m²/g, sold by the        company Sifraco.    -   filler (VII-D): silica AEROSIL® R812;

2) Preparation of the Compositions:

-   -   a) Preparation of a composition from a two-pack precursor:    -   A composition is obtained by mixing together, at room        temperature, 100 parts by weight of a part A and 10 parts by        weight of a part B of a two-pack system (see composition of        bi-component I and II in Tables I to IV).    -   b) The mixture is coated (deposited weight between 30 to 36        g/m²) to form a layer using doctor blades or rolls onto a        polyhexamethyleneadipamide fabric of desized 6.6 type with a        yarn count of 235 decitex (dtex) and having a contexture of        28.5×28.5 yarns/cm, and    -   c) the resulting layer is cured for 80 seconds at 180° C. in a        Mathis oven to obtain an elastomer. The results of the tests are        given in Tables V and VI.

Compositions I-1 to I-8 are compositions according to the invention.Compositions C-1, C-2, C-3 and C-4 are comparative. TABLE I Compositionof bi-component I (part A and B). Compositions C1 I-1 I-2 I-3 C-2 C-3Part A Number of parts by weight Composition containing 47.7 47.7 47.747.7 40 47.7 40% by weight of resin (V) and 60% by weight of diluent (A)Filler (VII-C) 0 0 0 0 32 16 Low-viscosity oil (I) 0 0 0 0 7 3.5High-viscosity oil (I) 45 40 27 19 13 29 Albacar © 5970 CaCO₃ 0 5 16 240 0 Oil (II) 6 6 6 6 6 6 VTMO 1 1 1 1 1 1 GLYMO 1 1 1 1 1 1 Part BComposition containing 45 45 45 45 45 45 40% by weight of resin (V) and60% by weight of diluent (A) High-viscosity oil (I) 51 51 51 51 51 51TBT 4 4 4 4 4 4 Catalyst (III) 0.02 0.02 0.02 0.02 0.02 0.02 Shore Ahardness test of the 33 36 42 52 52 40 elastomer obtained by combining100 parts of A and 10 parts of B, followed by curing at 150° C.-10 min

After mixing 100 parts by weight of part A and 10 parts by weigh of partB of bi-component I described in Table I, the resulting composition hasthe following contents of calcium carbonate and resin (V) (see TableII): TABLE II Compositions I-1 I-2 I-3 Calcium carbonate (1)  4, 5 14, 722, 1 albacar © 5970 % by weight relative to the total weight of themixture Résin (V) % by weight 18, 8 19, 2 19, 2 relative to the totalweight of the mixture

TABLE III Composition of bi-component II (part A and B) Compositions C4I-4 I-5 I-6 I-7 I-8 Part A (number of part by weight) Compositioncontaining 0 46 25.2 46.0 46.0 46.0 40% by weight of resin (V) and 60%by weight of diluent (A) Low-viscosity oil (I) 60.1 High-viscosity oil(I) 29.85 29.85 52.15 29.85 29.85 29.85 Calcium carbonate (1) 16.1016.10 Albacar © 5970 Calcium carbonate (2): 8.0 Socal © 31 Calciumcarbonate (3): 16.1 14.1 8.1 BLR3 © Filler (VII-d) Silica 5 2.0AEROSIL ® R 812 ECH (VI) 0.025 0.025 0.025 0.025 0.025 0.025 Oil (II)3.0 6 4.5 6 6 6 VTMO 1 1 1 1 1 1 GLYMO 1 1 1 1 1 1 Part B (number ofpart by weight) Composition containing 0 44.8 0 44.8 44.8 44.8 40% byweight of resin (V) and 60% by weight of diluent (A) High-viscosity oil(I) 51 51 51 51 51 51 Low-viscosity oil (I) 44.8 44.8 TBT 4 4 4 4 4 4Catalyst (III) 0.02 0.02 0.02 0.02 0.02 0.02 Shore A hardness test ofNot 45 28 39 43 41.5 the elastomer obtained by measured combining 100parts of A and 10 parts of B, followed by curing at 150° C.-10 min

After mixing 100 parts by weight of part A and 10 parts by weigh of partB of bi-component II described in Table III, the resulting compositionhas the following contents of calcium carbonate and resin (V) (see TableIV): TABLE IV Compositions I-4 I-5 I-6 I-7 I-8 Calcium carbonate (1)14.6 14.6 albacar © 5970 % by weight relative to the total weight of themixture Calcium carbonate (2): 7.3 Socal © 31 % by weight relative tothe total weight of the mixture Calcium carbonate (3): 14.6 12.8 7.4BLR3 © % by weight relative to the total weight of the mixture Résin (V)% by weight 18.4 9.2 18.4 18.4 18.4 relative to the total weight of themixture Filler (VII-d) Silica 1.8 AEROSIL ® R 812

TABLE V Results with a PA-6,6 fabric (batch 1, 235 dtex, 28.5 × 28.5yarns/cm, bi-component I) Compositions C1 I-1 I-2 I-3 C-2 C-3 Combingstrength (N) 525/523 580/560 730/693 840/820 700/650 650/630 (warp/weft)Improvement (%) relative to the 0 10.48 35.78 60 33 23.81 referencecomposition C1 Tearing strength (N) 189 150 142 121 75 85 Abrasionresistance (scrub test >1000 >1000 >1000 >1000 500 800 in cycles)

TABLE VI Results with a PA-6,6 fabric (batch 2, 235 dtex, 28.5 × 28.5yarns/cm, bi-component II) Compositions C4 I-4 I-5 I-6 I-7 I-8 Combing570 871 749 721 806 798 strength (N) (warp) Tearing 147 116 131 102 9499 strength (N) Abrasion >1000 >1000 >1000 >1000 >1000 >1000 resistance(scrub test in cycles)

(1) The test of resistance to creasing and to abrasion (“scrub” test)(ISO standard 5981 A) reflects the adhesion and the ageing behaviour ofthe composition. This test consists in subjecting the fabric firstly toa shear movement using two jaws pinching the two opposite edges of asample and driven in an alternating motion relative to each other, andsecondly to an abrasion by contact with a mobile support.

(2) The combing strength measurements are performed according to theindications of ASTM standard D 6479, (for determining the edgecombresistance of woven fabrics).

(3) The tear strength measurements are performed according to theprotocol of ISO standard 13937-2.

The best results are obtained for the system resin (V) and calciumcarbonate albacar© 5970.

Example 2

For the compositions C1 (Comparative) and I-2 (Invention), the proceduredescribed in Example 1, paragraphs 2 a) to c), is repeated for fabricsof polyhexamethyleneadipamide type of type 6.6 (PA-6,6), which arerepresentative of the market, and various conditions for curing theelastomer. The results are given in Table VII. TABLE VII Combing Combingstrength with strength with elastomer elastomer derived derivedContexture from from (warp/weft) Curing composition composition % FabricNumber of conditions C1 (N) I-2 (N) variance Dtex yarns/cm ° C./s WarpWeft Warp Weft (gain) 235 28.5 × 28.5 180 - 80 525 523 730 693 +36 35023 × 24 180 - 80 679 624 850 724 +20 350 23 × 24 180 - 30 650 627 857780 +28 350 23 × 24 200 - 30 692 625 869 845 +30 580 17 × 17 180 - 80452 469 550 506 +14 580 17 × 17 180 - 30 482 433 588 548 +24 580 17 × 17200 - 30 443 403 568 540 +31 580 16 × 16 180 - 80 373 419 526 515 +31580 16 × 16 180 - 30 365 358 454 454 +26 580 16 × 16 200 - 30 422 415532 465 +19

The gain in combing strength of formula I-2 is significant on a widevariety of cs with very different curing conditions (time andtemperature).

Example 3

Control Composition C-4

a) A control composition C-4 is prepared by mixing together 100 parts byweight of a part A and 10 parts by weight of a part B of a two-packsystem (see composition below). Compositions C4 Part A: Number of partsby weight Composition containing 25% by 47.7 weight of resin (V) and 75%by weight of diluent (B) Low-viscosity oil (I) 45.6 CaCO₃ 0 Oil (II) 6VTMO 1 GLYMO 1 Part B: Composition containing 40% by 45 weight of resin(V) and 60% by weight of diluent (A) High-viscosity oil (I) 51 TBT 4Catalyst (III) 0.02

-   -   b) A comparative test is performed between compositions I-2        (invention) and C-4 (comparative) which are coated onto fabrics        with different contextures (Table VIII). To do this, each        composition is coated, using a doctor blade depositing an amount        of about 50 g/m² to form a layer on the fabric; and

c) the resulting layer is cured for 80 seconds at 180° C. in aventilated oven to obtain an elastomer. The results of the tests aregiven in Table IX. TABLE VIII Nature of the test supports NaturePolyamide 6.6 Weight in g of 10 000 m of yarn 470 dTex Contexture 18 /18 (18 yarns in warp and weft per cm) Weight in g of 10 000 m of yarn470 dTex Contexture 16 / 16 (16 yarns in warp and weft per cm) Weight ing of 10 000 m of yarn 470 dTex, Contexture 13.5 / 13.5 (13.5 yarns inwarp and weft per cm)

TABLE IX Results Scrub Actual 1000 % % Coeff. Composition Reference g/m²cycles TSN Perf. CSN Perf. friction 18/18 Reference untreated fabric 232264 C-4 1 50 OK 446 +110  326 +23 1.8 I-2 2 52 OK 356 +70 433 +64 0.716/16 Reference untreated fabric 210 198 C-4 3 52 OK 387 +67 251 +26 2.8I-2 4 48 OK 347 +50 353 +78 0.8 13.5/13.5 Reference untreated fabric 178 36 C-4 5 50 OK 316 +77 127 +303  0.9 I-2 6 53 OK 311 +75 193 +467  1.1TS = tear strength (N)CS = combing strength (N)Scrub = abrasion resistance (scrub test in cycles)

-   -   Coefficient of friction (Ks): measurement of the coefficient of        friction according to ISO standard 8295.

The results show that the performance level of a coated 470 dtex 18×18fabric treated with composition C-4 has a combing strength comparable tothe 470 dtex 16×16 fabric treated with composition I-2 with entirelyacceptable performance qualities in terms of tear strength of the coatedfabric.

Furthermore, it is seen that a 13.5/13.5 reference untreated fabric thatis initially unusable for airbag applications on account of poor tearstrength properties (178 N) and poor combing strength properties (36 N),when treated by means of the process according to the invention, becomesentirely usable for applications in the field of airbags (tear strength:311 N/combing strength: 193 N).

1. Process for improving the combing strength and the tear strength of awoven, knitted or nonwoven fibrous support, comprising the followingsteps: a) the preparation of a curable silicone coating composition (A)comprising: components (a-1) or (a-2): (a-1) corresponding to at leastone polyorganosiloxane that may be cured by the action of a catalystbased on at least one organic peroxide, and (a-2) corresponding to apolyorganosiloxane blend that may be cured by polyaddition reactions,comprising: at least one polyorganosiloxane (I) containing, permolecule, at least two C2-C6 alkenyl groups linked to silicon, and atleast one polyorganosiloxane (II) containing, per molecule, at least twohydrogen atoms linked to silicon, an effective amount of curing catalystcomprising: when (a-1) is used, of at least one organic peroxide, andwhen (a-2) is used, of at least one metal (or compound) of the platinumgroup, optionally, at least one adhesion promoter (IV), and an additivesystem (B) for improving the combing strength and the tear strength, theconstituents of which are added sequentially or simultaneously,comprising a mixture of: at least one polyorganosiloxane resin (V)present at up to 60% by weight relative to the total weight of themixture and optionally mixed with at least one polyorganosiloxaneserving as diluent, and calcium carbonate (CaCO₃) present at up to 30%by weight relative to the total weight of the mixture; b) theapplication of at least 10 g/m², to one or two faces of a woven, knittedor nonwoven fibrous support of the silicone coating composition (A)prepared in step a), and c) the curing of the deposit formed in step b)to form an elastomer by heating to a temperature that may be up to 210°C., by electromagnetic radiation, in particular by infrared radiation.2. Process for improving the combing strength and the tear strength of awoven, knitted or nonwoven fibrous support according to claim 1, inwhich the curable silicone coating composition (A) comprises a mixtureformed from: (a) at least one polyorganosiloxane (I) containing, permolecule, at least two C2-C6 alkenyl groups linked to silicon, (b) atleast one polyorganosiloxane (II) containing, per molecule, at least twohydrogen atoms linked to silicon, (c) a catalytically effective amountof at least one catalyst (III), comprising at least one metal belongingto the platinum group, (d) at least one adhesion promoter (IV), (e) anadditive system (B) for improving the combing strength and the tearstrength, the constituents of which are added sequentially orsimultaneously, comprising a mixture formed from: at least onepolyorganosiloxane resin (V) present at up to 60% by weight relative tothe total weight of the mixture and optionally mixed with at least onepolyorganosiloxane serving as diluent, and calcium carbonate (CaCO₃)present at up to 30% by weight relative to the total weight of themixture; (f) optionally, at least one curing inhibitor (VI), (h)optionally, at least one coloration additive (VII), and (i) optionally,at least one additive (VIII) for improving the fire resistance. 3.Process for improving the combing strength and the tear strength of awoven, knitted or nonwoven fibrous support according to claim 1, inwhich the calcium carbonate is present in a proportion of from 4% to 26%by weight relative to the total weight of the mixture in the additivesystem (B).
 4. Process for improving the combing strength and the tearstrength of a woven, knitted or nonwoven fibrous support according toclaim 1, in which the calcium carbonate is present in a proportion offrom 10% to 24% by weight relative to the total weight of the mixture inthe additive system (B).
 5. Process for improving the combing strengthand the tear strength of a woven, knitted or nonwoven fibrous supportaccording to claim 1, in which the polyorganosiloxane resin (V) ispresent in the additive system (B) at up to 40% by weight, preferably ina proportion of from 5% to 30% by weight and most preferably of from 11%to 30% by weight relative to the total weight of the mixture.
 6. Processfor improving the combing strength and the tear strength of a woven,knitted or nonwoven fibrous support according to claim 2, in which theadhesion promoter (IV) of the curable silicone coating composition (A)exclusively comprises: (IV.1) at least one alkoxylated organosilanecontaining, per molecule, at least one C2-C6 alkenyl group, (IV.2) atlast one organosilicon compound comprising at least one epoxy radical,and (IV.3) at least one metal chelate M and/or a metal alkoxide ofgeneral formula: M(OJ)n, with n=valency of M and J=linear or branchedC1-C8 alkyl, M being chosen from the group formed by: Ti, Zr, Ge, Li,Mn, Fe, Al and Mg.
 7. Process for improving the combing strength and thetear strength of a woven, knitted or nonwoven fibrous support accordingto claim 2, in which the polyorganosiloxane resin (V) of the additivesystem (B) comprises siloxyl units Q of formula SiO_(4/2).
 8. Processfor improving the combing strength and the tear strength of a woven,knitted or nonwoven fibrous support according to claim 6, in which thepolyorganosiloxane resin (V) comprises in its structure from 0.1% to 20%by weight and preferably greater than 4% by weight of alkenyl group(s),the said structure containing identical or different siloxyl units oftype M, identical or different siloxyl units of type(s) T and/or Q, andoptionally siloxyl units of type D.
 9. Process for improving the combingstrength and the tear strength of a woven, knitted or nonwoven fibroussupport according to claim 7, in which the polyorganosiloxane resin (V)comprises at least 2% by weight and preferably at least 5% by weight ofsiloxyl units of type Q.
 10. Process for improving the combing strengthand the tear strength of a woven, knitted or nonwoven fibrous supportaccording to claim 2, in which the polyorganosiloxane (I) contains: (i)siloxyl units of formula: $\begin{matrix}{R_{a}^{1}Z_{b}{SiO}\frac{4 - \left( {a + b} \right)}{2}} & \left( {I\text{-}1} \right)\end{matrix}$ in which: the symbols R¹ represent an alkenyl group,preferably vinyl or allyl, the symbols Z, which may be identical ordifferent, each represent a monovalent hydrocarbon-based group, free ofunfavourable action on the activity of the catalyst and chosen fromalkyl groups containing from 1 to 8 carbon atoms inclusive, optionallysubstituted with at least one halogen atom, and also from aryl groups, ais 1 or 2, b is 0, 1 or 2 and the sum a+b is equal to 1, 2 or 3, andoptionally (ii) other siloxyl units of formula: $\begin{matrix}{{Zc}\quad{SiO}\frac{4 - c}{2}} & \left( {I\text{-}2} \right)\end{matrix}$ in which: Z has the same meaning as above and c is 0, 1, 2or
 3. 11. Process for improving the combing strength and the tearstrength of a woven, knitted or nonwoven fibrous support according toclaim 2, in which the polyorganosiloxane (II) comprises siloxyl units offormula: $\begin{matrix}{H_{d}L_{e}{SiO}\frac{4 - \left( {d + e} \right)}{2}} & \left( {{II}\text{-}1} \right)\end{matrix}$ in which: the groups L, which may be identical ordifferent, each represent a monovalent hydrocarbon-based group, free ofunfavourable action on the activity of the catalyst and chosen,preferably, from an alkyl group containing from 1 to 8 carbon atomsinclusive, optionally substituted with at least one halogen atom,advantageously from methyl, ethyl, propyl and 3,3,3-trifluoropropylgroups, an aryl group, and advantageously a xylyl, tolyl or phenylradical, d is 1 or 2, e is 0, 1 or 2, the sum d+e is equal to 1, 2 or 3,and optionally, at least some of the other units being units of meanformula: $\begin{matrix}{L_{g}{SiO}\frac{4 - g}{2}} & \left( {{II}\text{-}2} \right)\end{matrix}$ in which the groups L have the same meaning as above and gis equal to 0, 1, 2 or
 3. 12. Process for improving the combing strengthand the tear strength of a woven, knitted or nonwoven fibrous supportaccording to claim 2, in which the proportions of thepolyorganosiloxanes (I) and (II) are such that the molar ratio of thehydrogen atoms linked to silicon in (II) to the alkenyl radicals linkedto silicon in (I) is between 0.4 and 10 and preferably between 0.6 and5.
 13. Process for improving the combing strength and the tear strengthof a woven, knitted or nonwoven fibrous support according to claim 6,wherein the alkoxylated organosiloxane (IV.1) of the promoter (IV)corresponds to the following general formula:

in which formula: R1, R2 and R3 are identical or different hydrogenatedor hydrocarbon-based radicals and represent hydrogen, a linear orbranched C1-C4 alkyl or a phenyl optionally substituted with at leastone C1-C3 alkyl, U is a linear or branched C1-C4 alkylene, W is avalency bond, R4 and R5 are identical or different radicals andrepresent a linear or branched C1-C4 alkyl radical, x′=or 1, and x=0 to2.
 14. Process for improving the combing strength and the tear strengthof a woven, knitted or nonwoven fibrous support according to claim 6,wherein the organosilicon compound (IV.2) of the promoter (IV) ischosen: a) either from the products (IV.2a) corresponding to thefollowing general formula:

in which formula: R6 is a linear or branched C1-C4 alkyl radical, R7 isa linear or branched alkyl radical, y is equal to 0, 1, 2 or 3, and Xbeing defined by the following formula:

with: E and D, which are identical or different radicals chosen fromlinear or branched C1-C4 alkyls, z, which is equal to 0 or 1, R8, R9 andR10, which are identical or different radicals representing hydrogen ora linear or branched C1-C4 alkyl, and R8 and R9 or R10 alternativelyoptionally constituting, together and with the two carbons bearing theepoxy, a 5- to 7-membered alkyl ring, b) or from the products (IV.2b)which comprise epoxy-functional polydiorganosiloxanes comprising: (i) atleast one siloxyl unit of formula: $\begin{matrix}{X_{p}G_{q}{SiO}\frac{4 - \left( {p + q} \right)}{2}} & \left( {{IV}{.2}\quad{b1}} \right)\end{matrix}$ in which formula: X is the radical as defined above forformula (IV.2a) G is a monovalent hydrocarbon-based group, free ofunfavourable action on the activity of the catalyst and chosen fromalkyl groups containing from 1 to 8 carbon atoms inclusive, optionallysubstituted with at least one halogen atom, and also from aryl groups,p=1 or2, q=0, 1 or 2, p+q=1, 2 or 3, and (2i) optionally at least onesiloxyl unit of formula: $\begin{matrix}{G_{r}{SiO}\frac{4 - r}{2}} & \left( {{IV}{.2}\quad{b2}} \right)\end{matrix}$ in which formula G has the same meaning as above and r isequal to 0, 1, 2 or
 3. 15. Process for improving the combing strengthand the tear strength of a woven, knitted or nonwoven fibrous supportaccording to claim 6, wherein the metal M of the chelate and/or of thealkoxide (IV.3) is chosen from the following list: Ti, Zr, Ge, Li or Mn.16. Process for improving the combing strength and the tear strength ofa woven, knitted or nonwoven fibrous support according to claim 13, inwhich the adhesion promoter (IV) comprises a mixture of:vinyltrimethoxysilane (VTMO), representative of formula (IV.1),3-glycidoxypropyltrimethoxysilane (GLYMO), representative of formula(IV.2), and butyl titanate, representative of formula (IV.3). 17.Silicone coating composition curable by polyaddition reactions, forimproving the combing strength and the tear strength of a woven, knittedor nonwoven fibrous support, comprising mixture formed from: (a) atleast one polyorganosiloxane (I) containing, per molecule, at least twoC2-C6 alkenyl groups linked to silicon, (b) at least onepolyorganosiloxane (II) containing, per molecule, at least two hydrogenatoms linked to silicon, (c) a catalytically effective amount of atleast one catalyst (III), composed of at least one metal belonging tothe platinum group, (d) at least one adhesion promoter (IV), (e) anadditive system (B) for improving the combing strength and the tearstrength, the constituents of which are added sequentially orsimultaneously, comprising a mixture formed from: at least onepolyorganosiloxane resin (V) present at up to 60% by weight relative tothe total weight of the mixture and optionally mixed with at least onepolyorganosiloxane serving as diluent, and calcium carbonate (CaCO₃)present at up to 19% by weight relative to the total weight of themixture; (f) optionally, at least one curing inhibitor (VI), (h)optionally, at least one coloration additive (VII), and (i) optionally,at least one additive (VII) for improving the fire resistance. 18.Precursor two-pack system (C) for the silicone coating composition (A)according to claim 17, comprising: two separate parts A and B, which areintended to be mixed together to form the composition, and one of theseparts A or B comprising the catalyst (III) and only onepolyorganosiloxane species (I) or (II).
 19. Woven, knitted or nonwovensupport coated on one or two faces with an elastomer that may beobtained: a) by applying at least 10 g/m² onto one or two faces of awoven, knitted or nonwoven fibrous support of the silicone coatingcomposition (A) according to claim 17 or of the composition resultingfrom mixing the parts A and B of the two-pack system (B) according toclaim 18, and curing the deposit formed in the preceding step to form anelastomer by heating to a temperature that may be up to 210° C. or byelectromagnetic radiation, in particular by infrared radiation, or b) bythe process according to claim
 1. 20. Support according to claim 19,characterized in that the fibrous support is a fabric with an opencontexture having a porosity >10 l/dm²/min according to ISO standard9237.
 21. Inflatable bag for protecting an occupant of a vehicle, formedfrom a support coated according to claim
 19. 22. Use of the two-packsystem (B) according to claim 18 or of a curable silicone coatingcomposition (A) according to claim 1 for coating a woven, knitted ornonwoven fibrous support.
 23. Use according to claim 22, for coatingsupports intended to form inflatable bags for protecting the occupantsof vehicles.
 24. Use according to claim 22, wherein the support is afabric with an open contexture having a porosity >10 l/dm²/min accordingto ISO standard 9237.